Effect of Organic Matter and Incubation Time on Pb Chemical Forms in a Calcareous Soil

This study was conducted to investigate the effect of non-living Spirulina cyanobacterium (Arthrospira platensis) biomass as an organic matter and incubation time on the chemical forms of lead (Pb) in a calcareous soil. The experiment was conducted in a factorial with completely randomized design in three replications. Treatments consisted of two incubation time (one and two months at 25 oC), three Pb levels as Pb(NO3)2 (control (10), 200, and 400 mg kg-1 of soil) and three Spirulina cyanobacterium levels (0, 500 and 1000 mg kg-1 soil). Results showed that with increasing Pb levels, Pb concentration in all chemical forms (Ex, Car, Om, Fe-ox, Mn-ox and Res-Pb) significantly increased. Different levels of Spirulina cyanobacterium had different effects on Pb chemical forms over time but, in general, application of Spirulina increased Ex and Car-Pb fraction by 31% and 43%, respectively as compared to those of control, and increased Pb availability in the soil. Therefore, application of this cyanobacterium as an amendment should be done with caution; and more investigation at different incubation time and different soils are recommended.